LEGG, MARK R., ACTA, Inc., Torrance, CA, THOMAS K. ROCKWELL, San Diego State University, San Diego, CA, and ELDON M. GATH, Leighton & Associates, Diamond Bar, CA

ABSTRACT: Active Faulting Along California's Southern Coast

California's Southern Coast lies within the active dextral transform plate boundary between the Pacific and North America plates, where numerous faults associated with the San Andreas fault system pose a serious earthquake threat to this heavily developed area. Active faults are those expected to experience potentially damaging earthquakes under the current tectonic environment. Thus, all faults with evidence of late Quaternary deformation should be considered active. Buried faults are included if the overlying late Quaternary sediments can be shown to have suffered deformation as a result of the deeper fault movement or if well-defined bands of seismicity are associated with the structure. Active faulting in the Southern Coast region may be divided into several northwest-trending str ke-slip fault zones. Because of changing plate-motion vectors and local fault geometry, components of oblique slip, including both transtension and transpression, are found throughout this region. From west-to-east, the major fault zones include the San Clemente, Catalina-San Diego Trough, San Pedro Channel, Palos Verdes-Coronado Bank, Newport-Inglewood-Rose Canyon, Vallecitos-San Miguel, and Whittier-Elsinore zones. Several historically damaging earthquakes have occurred along faults of the Southern Coast region with the greatest damage associated with those faults underlying or in close proximity to urban areas. Similar to what is expected from large earthquakes on the San Andreas fault, large earthquakes on deep-water offshore faults may generate strong ground shaking along the southe n California coastal region. In addition, they pose the additional threat of locally generated tsunamis.

AAPG Search and Discovery Article #90992©1993 AAPG Pacific Section Meeting, Long Beach, California, May 5-7, 1993.